The invention relates to a device with a rotating separating element and a method for conveying and separating a suspension with biological cells or microorganisms in biological processes. It also relates to a bioreactor with a conveying and separating device of this kind. Continuous cell separation or particle separation of human, animal, plant or hybrid culls, micro-organisms or of carriers populated with cells (micro-carriers) in biological processes is a crucial object. Cell culture techniques consequently have to meet very high requirements, in particular when cultivating sensitive mammal cells. This is illustrated, for example, in the article "Langzeitkultivierung von Saugetierzellen" ("Long-term cultivation of mammal cells") in Technische Rundschau SULZER 3, 1990, pp. 24-28, in which a perfusion reactor with a rotating spin filter (MBR Spinferm Bioreaktor) is also described as the most recent prior art. The purpose of separating cells and medium is to retain cells in the bioreactor in order to achieve high cell densities, to continuously pass fresh nutrient medium through the cells and at the same time remove the product and toxic metabolites and simplify the processing of the active substances such as hormones, antibodies or vaccines, which nee separated from the cells and which have to be drawn off free from cells. The highly sensitive mammal cells have to be kept constantly in an optimum environment with a sufficient supply of nutrients and, in particular, oxygen, Absolute sterility must be maintained in the entire reaction area, while the cells, which are highly sensitive to shear forces, must not be exposed to any high mechanical stresses. Although the described perfusion reactors with a rotating spin screen represent a significant improvement on conventional filter and separating systems, cells even accumulate on the rotating screen of these reactors. This ultimately leads to clogging of the screen and the accumulation of dead, decomposing cells. Although coarser spin filters reduce the degree of clogging, the selectivity of the separation is at the same time impaired. External centrifuges are hardly suitable for separating sensitive cells on account of long feed lines, restricted oxygen supply, excessive mechanical stresses and insufficient sterility as regards the seals of moving parts.